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How comets break up and make up

For some comets, breaking up is not that hard to do. A new study indicates that the bodies of some periodic comets — objects that orbit the Sun in less than 200 years — may regularly split in two, then reunite down the road. This may be a repeating process fundamental to comet evolution.

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No large caverns found inside Comet 67P

Comets are known to be a mixture of dust and ice, and if fully compact, they would be heavier than water. However, measurements have shown some of them to have densities much lower than that of water ice, implying that comets must be highly porous. A new study of low-density Comet 67P/Churyumov-Gerasimenko using data from ESA’s Rosetta spacecraft rules out a cavernous interior.

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Rosetta’s first peek at comet 67P’s dark side

Since its arrival at comet 67P/Churyumov-Gerasimenko in August 2014, ESA’s Rosetta spacecraft has been surveying the surface and the environment of this curiously shaped body. Now that the comet is experiencing a brief, hot southern hemisphere summer, its south polar regions have emerged from almost five years of total darkness and it has been possible to observe them with other Rosetta instruments.

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Rosetta studies Comet 67P at perihelion

ESA’s Rosetta spacecraft has witnessed 67P/Churyumov–Gerasimenko make its closest approach to the Sun (perihelion) at 3:03am BST on 13 August, when the comet came within 116 million miles of our nearest star. Rosetta’s measurements suggest the comet is currently spewing up to 300kg of water vapour and a metric tonne of dust every second, creating dangerous working conditions for the spacecraft.